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Posted: Jan 09, 2009 8:37:30 pm
gwynsms



Porsche 964 Set-up. Jan 4th 2009.

I was recently commssioned to do a full suspension setup on a left hooker 1991 Porsche 964,
3.6 engine.The car is a very nice example and has been proudly owned by Katherine (Babs) for
some months now. The motive for doing a setup was twofold; a) it has adjustable coil over
suspension fitted by its previous owner and b) its hard work getting it to turn in when on
track. Additonally, its due a new set of boots soon, with old ones showing signs of some
uneven wear. The car is both road use and regular track day visits.

So as usual, got the scales ready for a corner weigh; total weight with half a tank of fuel
was 1345kgs, thats the easy bit. Balance across the front axle was within a respectable
9kgs, but as usual on 911 types we had a rear axle imbalance, nearly 40kgs for this car.
Unusually, the right rear was heavy despite driver on board and sat on the "wrong" side!
Okish but could be better! This gave us a diagonal crossweight of 51.6%/48.4%, a bit over my
target of 50.8/49.2.

No probs sorting this we thought, we got adjustable spring platforms all round haven't we,
no torsion bar spring plates to fight with. So we enthusiastically dived into RR to lower
this corner a bit. Well, our enthusiasm was short lived as we found the platform nearly at
its minimum, but managed to get 3/4 of a turn out of it. A small improvement. Ok, lets lower
LF then. Bugger, this is at min as well and pretty seized up!! Whoever chose these posh
springs  (progressive ones) got their free length calcs wrong... Plan C then; was raise LR a
bit and hey presto we got diagonal distribution of 50.6% and 49.4%, pretty good for a 1345kg
car.

Now let me remind you that this beasty is reluctant at turning in. We hadn't yet got a
satisfactory explanation for this phenomon, but the next bit explained all.

So, replaced the corner weight scales with turn plates and on with infra red aligner
sensors. Did a front caster check to get a baseline set of data and fired up the "Virtual
view" of all 4 wheels. This was a picture as we had shed loads of toe-in both front and
rear, but to be fair rear thrust angle was spot on zero. We used the library data for a P911
Carrera RS and rear toe was almost maximum allowed by Porsche, and makes the car pretty
"granny" proof for toddling down to Tescos!

The 964 has redesigned versions of trailing arm v older 911s, with the eccentric adjusters
on the inboard leg of each arm. Optimism setin again as we thought these will be easy to do
with toe doing toe and camber doing camber! After a fight with seized and innaccessible
bolts, we found that camber ajduster dramatically changes toe! After some mutterings,
acheived max available neg camber on RR but still a bit shy of Porsche's prefferred values,
at 48' v desired 1deg 5'. Then set rear toe-in to 5' each side from the 19' we started with.
This should make it turn in niceley without too much drama on the road.

Next we turn our attention to the front, and, we actually had positive camber on RF, LF was
fine at 1deg neg. According to the guide/illustrations on the aligner database, front camber
has eccentric adjusters at the bottom of the strut, except our car hasn't!! Ok, we've got
elongated holes, so a bit of marking, levering and guessing and we acheive some 30' of neg
camber and decided to accept this. (why? could be the subject of a seperate report all of
its own...) So to finalise the set up, we centralised the steering wheel and set front toe
to 5' toe in each side (was 15ish when we started), 5' in should be comfortable on the road.

So what now. Well the next track day will give me feedback to see if we've acheived our targets.

After a long cold day, pretty happy with the results. I then retired indoors, and settled
into reading my Xmas gift of a textbook on Quantum Theory; no I'm not joking I'm just sad!!!

Gwyn
SMS Motorsport
"where there's a will, there's an engineering solution"

Posted: Mar 21, 2009 10:00:07 pm
Pete



Nice one Gwyn

My car is now ready for a proper corner weight and balance.  RSR suspension and RSR spring plates are fited and all ready for your scales and laser aligner.  Let me know when you are ready.


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